JPH1080186A - Motor driving equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To surely reduce a coil current during current OFF command term. SOLUTION: This motor driving equipment supplies a desired coil current to a motor coil, by pulse-width-controlling either one of motor driving transistors of a power supply side and a ground side. In OFF command term in which a coil current is reduced and during OFF term of the motor driving transistors, both the transistors of the power supply side and the ground side are subjected to OFF control, both sides driving is performed from when the OFF term is started to when the level of coil current is decreased to a specified level, and a coil current is rapidly reduced. A second comparator compares the level of a coil current, e.g. a CR output waveform corresponding to the coil current level with a specified switching level V2, and generates a switching detecting signal when the CR output waveform becomes equal to or lower than V2. Thereby transfer is performed to single side driving in which either one of the motor driving transistors of the power supply side and the ground side is subjected to OFF control, and the coil current is gently reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a motor driving device for controlling a motor driving transistor by a pulse width control method and supplying a coil current according to a target value to a motor coil.

[0002]

2. Description of the Related Art In various motors, for example, a motor driving device for a stepping motor, a driving device for controlling a coil current flowing through a motor coil by a pulse width control method (hereinafter referred to as a PWM control method) has been known. The PWM control method includes a one-side chopping method (one-side drive) in which only one of a power supply side and a ground side drive transistor for supplying a coil current to a motor coil is PWM-controlled, and a power supply side and a ground side drive. Two types of a double-sided chopping method (both-side driving) in which both transistors are PWM-controlled are known.

Hereinafter, these two driving methods will be described with reference to FIGS. 5 and 6. FIG.

FIG. 5 shows a driving example in the case of the one-side chopping method. In this example, the motor driving transistor on the power supply side is PWM-controlled. In the case of the one-side chopping method, for example, as shown in FIG. 5A, during a predetermined transistor ON period, of the motor drive transistors Q1 to Q4 of the coil LM of a certain phase, the drive transistor Q3 on the power supply side and the drive transistor Q3 on the ground side The drive transistor Q2 is turned on, and as a result, the motor coil LM is turned on as shown by the solid arrow.
, A coil current IM flows.

When the on-period ends and the off-period ends, the on-state of the transistor Q2 is maintained as it is, and only the transistor Q3 has the P-level as shown in FIG.
The off control is performed by the WM control signal. Here, even if the motor drive transistor is turned off, the motor coil L
Since M tries to supply more current, the diode D4 is turned on, and as shown by the dotted arrow, passes through the motor coil LM and the transistor Q2 in the ON state, and further passes through the resistor Rdec for detecting the coil current. The coil current IM flows toward ground.

The coil current IM gradually decreases during the off-period as shown in FIG. 5 (b), and after the off-period elapses for a certain period of time, one of the power supply-side or ground-side motor drive transistors is turned on again. Controlled (here, the power supply (V
When the transistor Q3 on the BB) side is controlled to be ON), the coil current IM flows as shown by the solid line arrow, and the amount of current rapidly increases.

As described above, for example, by performing PWM control of the transistor Q3 on the power supply side at a predetermined timing,
The coil current flows through the motor coil LM with a waveform as shown in FIG.

Next, in the both-side chopping method, FIG.
As shown in (a), during the ON period of the motor drive transistor, first, as in the case of one-side chopping, both the power supply side and the ground side motor drive transistors Q3, Q2
Is turned on, and the coil current IM is
Flows. In the off period of the motor drive transistor, both the power supply side and the ground side motor drive transistors Q3 and Q2 are connected to each other as shown in FIG.
Off control is performed by a PWM control signal as shown in FIG. Accordingly, during the off period, the diodes D4 and D1 are turned on, and the coil current IM flows from the ground to the power supply VBB as indicated by the dotted arrow in FIG. 6A.

As described above, in the case of the double-sided chopping method, both the power supply side transistor and the ground side transistor are turned off during the off period of the transistor.
As shown in (b), the coil current during the off-period decreases more rapidly than in the one-side chopping method.

[0010]

In the one-side chopping method of the above two methods, as apparent from FIG. 5 (b), the decrease in the coil current during the off period is gradual. For this reason, the ripple component of the coil current waveform is reduced, but the drive transistor is set to the PW
Due to the M control, the coil current does not decrease sufficiently during a certain OFF period, and the actual coil current waveform deviates from the set target waveform (dotted line in the figure) as shown in FIG. There was a problem that it would.

In the case of one-sided chopping method,
Because the coil current drops sharply during the off period,
Although the problem of deviation from the target waveform as in the one-sided chopping method does not occur, since the amount of current is always greatly reduced during the transistor off period, FIG.
There is a problem that the ripple component of the coil current waveform becomes large as shown in FIG.

Therefore, it has been proposed to switch and execute both of these two methods to suppress the ripple and increase the amount of decrease in the coil current during the off period to eliminate the deviation from the set waveform. However, no specific proposal has been made on a method of appropriately switching between these two types of switching. In particular, as a motor drive device which is increasingly integrated, there is no known device that easily and easily switches the method on an IC at an appropriate timing.

For example, as a switching type motor driving device, it is conceivable that the switching between the two chopping types is made by another circuit such as an external circuit, but when the switching is executed by such an external circuit, However, an external circuit is required separately, and an operation of adjusting the external circuit is required, which is not preferable.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems, and has a simple configuration and a motor driving device capable of easily switching between two PWM control systems at appropriate timing to drive a motor coil. The purpose is to provide.

[0015]

In order to achieve the above-mentioned object, a motor driving device according to the present invention has the following features.

That is, a motor driving device for supplying a desired coil current to a motor coil by controlling the pulse width of one of a power source side and a ground side motor driving transistor. In the current off command period, during the off period of the motor drive transistor, both the power supply side and the ground side motor drive transistor are turned off from the start of the off period until the coil current level decreases to a predetermined level. The two-sided drive is performed under control, and when the level of the coil current becomes equal to or lower than the predetermined level, the drive is switched to the one-sided drive in which only one of the power supply side and the ground side motor drive transistors is turned off.

As described above, in the present invention, during the period in which the coil current has to be reduced, both-side driving, that is, both the power supply side and the ground side are performed with reference to the point in time when the coil current level falls to a predetermined level. The control is switched from the off control of the motor drive transistor to the normal one-side drive, that is, the off control of only one of the power supply side and the ground side motor drive transistors.

In executing the above control, a more specific configuration includes a current detecting means for detecting a coil current, and a current amount detected by the current detecting means being compared with a target value to be equal to or more than a target value. , A target value comparison means for generating a target arrival signal, an off-period measurement means for generating an off-period elapsed signal after a lapse of a certain period from the generation of the target arrival signal, and the coil current according to the target arrival signal. An output drive unit for controlling the supply of the motor drive transistor to off and controlling the motor drive transistor in accordance with the off-period elapse signal to control the pulse width of the motor drive transistor; and a signal corresponding to the level of the coil current. Is compared with a switching reference value, and a switching signal is generated when the switching reference value is lower than the switching reference value. In the current off command period, the power supply side and ground side motor drive transistors are driven on both sides based on the target arrival signal, and the power supply side and ground side motors are driven in accordance with a switching signal from the switching reference comparison means. The driving transistor is switched to one side driving.

As described above, during the off-period of the motor drive transistor within the current-off command period, by controlling the switching between the two-sided drive and the one-sided drive, the ripple component is greatly increased in the coil current waveform obtained as a result of the control. Without this, it becomes easy to rapidly and sufficiently reduce the coil current.

Further, in the present invention, there is also provided a motor drive device for supplying a desired coil current to a motor coil by controlling a pulse width of one of a power supply side and a ground side motor drive transistor. In the current off command period for decreasing the current, after the start of the off period of the motor drive transistor, the off period of the motor drive transistor is continued until the level of the coil current decreases to a predetermined off target value, The off control by the motor drive transistor is switched to the on control.

Further, according to the present invention, there is provided a motor driving device having the above-mentioned configuration, further comprising: in a current-off command period, a constant-off period of a motor-driving transistor and switching control between two-sided driving and one-sided driving during the off-period. And a level priority mode in which the off period continues until the coil current level decreases to a predetermined off target value. Here, when the mixed mode is set, within a certain OFF period of the motor driving transistor, both side driving of the motor driving transistor and one side driving are controlled to be switched, and conversely, when the level priority mode is set, Generation of an off-period elapse signal for stopping the switching operation between the two-sided drive and the one-sided drive of the motor drive transistor and terminating the off-period of the motor drive transistor until the coil current decreases to reach an off target value. Is stopped.

By executing the level priority mode,
Low current control of the coil current is ensured. Then, by setting and executing one of the mix mode and the level priority mode according to the motor to be driven, it is possible to perform appropriate motor drive control according to the conditions.

[0023]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic block diagram of an IC of a motor drive device according to the present embodiment.

In the motor driving apparatus of the present embodiment, as a basic control method, a one-side driving method in which one of the power source side and the ground side motor driving transistors Q1, Q3 and Q2, Q4 is PWM controlled is adopted. (In this embodiment, the motor drive transistor on the power supply side is controlled).

The switching of the motor drive transistors Q1 to Q4 for supplying a desired coil current IM to each motor coil is performed by a control signal from the output drive unit 22. In the PWM control of turning on and off the motor drive transistors Q1 to Q4 in the output drive unit 22, first, the start timing of the off period of the motor drive transistor is determined by the first comparator 12 using the target value V1 and the detection coil current according to the operation command. In comparison, the output is determined by the target arrival signal. The end of the off-period, that is, the start timing of the on-period of the motor drive transistor is determined by an off-period elapse signal output from the one-shot circuit 14.

The first comparator 12, which determines the start of the off period of the transistor, has one input terminal connected to the motor drive control section 10, and the other input terminal connected to the ground side motor drive transistor Q2. It is connected between the emitter of Q4 and the coil current detecting resistor Rdec. Further, the motor drive control unit 10 responds to the drive command of the motor supplied to the input terminal IN, and
One input terminal of the comparator 12 is provided with a motor coil L
A target waveform (target value V1) of the coil current to be supplied to M is supplied. Note that the target waveform may be a waveform created by the motor drive control unit 10 in response to the operation command, and when the operation command indicates a target waveform, the operation command may be used as the target waveform. Is also possible.

The first comparator 12 calculates the target value V1 of such a target waveform supplied from the motor drive control unit 10.
Is compared with the detection coil current detected by the coil current detection resistor Rdec. When the detection coil current reaches the target value V1, a target arrival signal is generated. The target arrival signal is output to the output drive unit 2 via the one-shot circuit 14.
2, and the output drive unit 22 starts off control of a predetermined motor drive transistor in accordance with the target arrival signal.

The one-shot circuit 14 has a configuration in which an external capacitor C1 is provided at the CR terminal. When a target arrival signal is supplied from the first comparator 12, charging of the capacitor C1 is stopped in response to the supply. Then, the capacitor C1 is discharged at a predetermined speed. When the output voltage from the capacitor C1 becomes equal to or lower than a predetermined level after a lapse of a certain period from the start of the discharge, this is detected, and an off-period lapse signal is generated. The off-period elapse signal is supplied to the output drive unit 22, and the output drive unit 22 ends the off-control of the predetermined motor drive transistor and starts the on-period again according to this signal.

In this embodiment, in addition to the above configuration, a second comparator 16 for comparing the output of the capacitor C1 with a predetermined switching reference value V2 is provided in the same IC. On the output side of the second comparator 16, a gate circuit 18 for controlling the operation of the second comparator 16 according to a mode described later, and a switching circuit 20 for controlling the output from the gate circuit 18 according to the set mode. Is provided. However, the gate circuit 18 is not limited to the output side of the second comparator 16 and may be provided inside the second comparator 16 or on the input side to the second comparator 16.

Here, one input terminal of the second comparator 16 is supplied with a switching reference value V2 set by external resistors Rref1 and Rref2. The other input terminal is connected to a CR terminal indicating the charging voltage (CR output waveform) of the capacitor C1. The second comparator 16 outputs a CR output waveform from the CR terminal corresponding to the level of the coil current. Is compared with the mode switching reference value V2, and when the CR output waveform becomes equal to or less than the mode switching reference voltage V2, a switching detection signal is output. The switching detection signal determines the timing of switching from the both-side off control to the motor driving transistor to the one-side off control during the transistor off period in the current off command period.

The above-mentioned motor drive control unit 10 creates, for example, a target waveform of a coil current corresponding to the operation command from the operation command, determines an operation mode in the drive device, and, based on the determination result, One shot circuit 1
4 is supplied with a control signal. Further, in FIG. 1, the control signal is directly supplied to the gate circuit 18 and the switching circuit 20 from the outside, but the present invention is not limited to this.
The motor drive control unit 10 may be configured to supply a control signal.

Here, in the present embodiment, the characteristic mode as the set operation mode is to control the motor drive transistor to turn off after a certain period has elapsed from the start of turning off the motor drive transistor. This is a mix mode in which control and one-side control are switched and executed. As another mode, a level priority (sense priority) in which the transistor OFF control period is continued until the detected coil current decreases to a predetermined level.
The mode can be set.

[Operation in Mixed Mode] Even when the mixed mode is selected as the operation mode, the motor driving apparatus according to the present embodiment is used during the coil current ON command period and during the transistor ON period of the OFF command period. Works normally. In other words, during these periods, one-side drive is performed in which only one of the power supply side and the ground side of the motor drive transistors Q1 to Q4 is PWM-controlled to control the coil current.

On the other hand, in the transistor-off period of the current-off command period, at the start of the off-period, the motor drive transistors on both the power supply side and the ground side are turned off to rapidly reduce the coil current. When the coil current level decreases to a certain level (specifically, the CR output waveform changes to the switching reference value V2), only one of the motor driving transistors is turned off to return to a so-called one-sided driving state.

Hereinafter, the operation of the motor driving device in the mixed mode will be specifically described with reference to FIGS. 2 and 3.

The waveform shown in FIG. 3A is a target waveform of the coil current when a sine wave is used, and the current off command period of the coil current corresponds to the hatched portion of the waveform. The current-off command period is performed, for example, by a microcomputer (not shown) from the motor drive control unit
For 0, it is determined by supplying a control signal as shown in FIG. 3B as an operation command. Or
3B based on the operation command.
Is determined by creating a control signal such as

When a predetermined motor drive transistor is turned on when such a current-off command is given, as shown in FIG. 2A, during this transistor-on period, the detection coil current IM reaches the target Continue until the value exceeds V1. When the first comparator 12 exceeds the target value V1, a target reaching signal (L level output in this example)
This causes the off period to start. Therefore, the motor drive transistors on both the power supply side and the ground side are turned off. The two-sided driving at this time is executed by outputting a two-sided driving signal from the second comparator 16 via the switching circuit 20 or the gate circuit 18, for example. Further, the motor drive control unit 10 may output a similar double-sided drive signal to the output drive unit 22.

When the coil current IM flows as shown by the solid line in FIG. 1, the motor drive transistors Q3 and Q2 on both the power supply side and the ground side are turned on. Then, during the current-off command period, when the target arrival signal is generated by the first comparator 12 and the transistor-off period starts, the output drive unit 22 first outputs the two transistors Q3, Q2 according to the target arrival signal. Both are turned off, that is, both-side control is started. As a result, the coil current flows through the diodes D4 and D1 as shown by the dotted line in FIG. 1, and the coil current rapidly decreases as in the conventional double-sided chopping method (see FIG. 2A).

Since the one-shot circuit 14 starts discharging the capacitor C1 in response to the target arrival signal from the first comparator 12 as shown in FIG. 2B, the waveform at the CR terminal is as shown in FIG. 2C. At the same time as the start of the transistor off period.

The second comparator 16 operates as shown in FIG.
Is reduced to the switching reference level V2,
As shown in FIG. 2E, a switching signal (here, L level output) is generated. The switching signal is supplied to the output drive unit 22 via the gate circuit 18 and the switching circuit 20, and the output drive unit 22 responds to the output signal, for example, as shown in FIG.
As shown in (1), one of the motor drive transistors Q3 and Q2 (here, the motor drive transistor Q3) on the power supply side and the ground side, which has been turned off by the double-sided drive, is turned off to switch to the single-sided drive.

By switching to the one-side drive, the current is reduced as shown in FIG.
, And the coil current decreases more gradually than in the both-side driving period, similarly to the conventional one-side chopping method.

The one-shot circuit 14 outputs an off-period elapsed signal (here, an L-level output) when the CR output waveform reaches a predetermined off-end level V3 from the start of turning off the transistor (FIG. 2 (d)). reference). Here, since the CR output waveform shown in FIG. 2 (c) decreases at a constant rate from the start of discharging of the capacitor C1, the off-period end timing is determined based on this CR output waveform, so that the off-period is determined. Is controlled to be constant.

When an off-period elapsed signal is output from the one-shot circuit 14, the output drive section 22 ends the off-period of the transistor and starts on-control. For this reason, the coil current increases again from the start of the ON control.

When the coil current increases due to the on-control and reaches the target value V1 at the next timing, the first current is returned again.
The comparator 12 generates the target arrival signal, and the motor drive transistor is turned off in the same manner as described above. During this off period, the switching control from double-sided drive to single-sided drive is performed.

In the current-on command period, FIG.
As shown in (a) and (b), the coil current is controlled by a one-sided driving method capable of reducing the ripple component of the coil current as in the related art. Then, as described above, only during the current-off command period, mixed drive of both-side drive and one-side drive is performed during the transistor-off period. By performing the mixed driving during the transistor off period during the current off instruction period, the coil current can be rapidly reduced during the current off instruction period.

In the present embodiment, the timing of switching from double-sided drive to single-sided drive is determined not by the detected coil current but by comparing the CR output waveform corresponding to this coil current level with the switching reference level V2. I decided that. Although it is not necessary to determine by comparing with the CR output waveform, as shown in FIG. 2C, the charge output of the capacitor C1 is within a certain range regardless of the level of the coil current. Makes it possible to always use a constant level V2 determined by the resistors Rref1 and Rref2 as a switching reference.

When a coil current waveform as shown in FIG. 3C is used instead of a sine wave coil current waveform as shown in FIG. 3A, the current-off command period is, for example, as shown in FIG. ) Is set as a period in which the coil current level decreases from a predetermined coil current level to the next lower coil current level. Then, if the mix drive is performed during the transistor off period during the current off command period,
The same effect as above can be obtained. Further, during the period in which the coil current is maintained at a constant level, by performing the one-side drive, the ripple component of the coil current can be suppressed to a low level.

[Operation in Sense Priority Mode]
The operation in the sense priority mode will be described.

In this embodiment, the off-period of the motor drive transistor is fixed when performing one-sided driving in both the mixed mode and the current-on command period. In contrast, in the sense priority mode, the end timing of the transistor off period is determined by determining whether the coil current has decreased to a predetermined level. The sense priority mode is set when the coil current is reduced to a sufficiently low level during the current off command period.

FIG. 4 shows the operation of the motor drive device of FIG. 1 in the sense priority mode. When the sense priority mode is set, this mode command is supplied to the motor drive control unit 10 as a motor operation command or a direct control signal, and the gate circuit 18 and the switching circuit 2
0 is also supplied.

As shown in FIG. 4 (a), the first comparator 12 compares a detected waveform with a target waveform corresponding to an operation command supplied from the motor drive control unit 10, and determines a detected value. When V1 or more, a target arrival signal (here, L level output) is generated. Since the switching circuit 20 and the gate circuit 18 are switched to the sense priority mode, the output from the second comparator 16 during the transistor off period of the current off command period is prohibited.

Accordingly, the output drive unit 22 controls off (one-side drive) one of the power supply side and the ground side motor drive transistors based on the target arrival signal. Thereby, for example, the coil current indicated by the solid line in FIG. 1 flows as indicated by a dashed line.

The one-shot circuit 14 starts measuring the off period based on the target arrival signal from the first comparator 12. However, since the sense priority mode command is supplied from the motor drive control unit 10, FIG.
4D, the output is prohibited even if an off-period elapsed signal is obtained after a certain period has elapsed as shown by the dotted line in FIG. 4D.

Here, the first comparator 12 has a hysteresis characteristic. For this reason, when the detection coil current reaches the operation target V1, the first comparator 12 outputs, for example, an L level (target reaching signal). When the detection coil current falls below the desired off target value V4, an H level (off target reaching signal) is output. For this reason, the motor drive transistor is first turned off by the generation of the target arrival signal, and when the coil current decreases to a predetermined off target value V4 or less, the first comparator 12
Output the off target arrival signal.

In the one-shot circuit 14, the supply of the off target reaching signal cancels the output of the off-elapse signal, and the off-period elapse signal (here, L level) at the timing shown in FIG. (Output) and supplies it to the output drive unit 22. Therefore, the output drive unit 2
2 turns on the motor drive transistor again.

It should be noted that a comparator for comparing the off target value V4 with the detection coil current may be provided separately.
Control in the sense priority mode is possible. In this case, it is not necessary to provide the first comparator 12 with the above-described hysteresis characteristics.

[0058]

As described above, according to the motor driving apparatus of the present invention, during the current-off command period, during the off-period of the motor driving transistor, both-side driving of both the power-supply-side and ground-side motor driving transistors is performed. By switching to one of the two driving modes, the coil current can be rapidly reduced within a certain OFF period. Further, the ripple component of the coil current can be reduced to a sufficiently low level as compared with the case of only driving on both sides.

If the level priority mode can be set, low-current control of the coil current can be easily performed. By setting a mix mode in which both-side drive and one-side drive are performed and a level-priority mode, the mode can be selected according to the conditions of the motor to be driven. Can be improved.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a schematic configuration of a motor drive device according to an embodiment of the present invention.

FIG. 2 is a time chart for explaining an operation in a mixed mode according to the embodiment of the present invention.

FIG. 3 is a time chart for explaining a relationship between a target waveform of a coil current and a current off command period in the embodiment of the present invention.

FIG. 4 is a time chart for explaining an operation in a sense priority mode according to the embodiment of the present invention.

FIG. 5 is a diagram illustrating a one-side chopping method of a conventional motor drive device.

FIG. 6 is a diagram illustrating a both-side chopping method of a conventional motor drive device.

[Explanation of symbols]

10 motor drive control unit, 12 first comparator, 1
4 One-shot circuit, 16 Second comparator, 18
Gate circuit, 20 switching circuit, 22 output drive unit.

Claims (4)

[Claims] 1. A motor drive device for supplying a desired coil current to a motor coil by controlling a pulse width of one of a power source side and a ground side motor drive transistor, the motor drive device comprising: In the current off command period, during the off period of the motor driving transistor, both the power supply side and the ground side motor driving transistor are turned off from the start of the off period until the level of the coil current decreases to a predetermined level. Motor driving is performed, and when the level of the coil current becomes equal to or less than the predetermined level, the driving is switched to one-sided driving in which only one of the power supply side and the ground side motor drive transistors is turned off. apparatus. 2. The motor driving device according to claim 1, wherein: a current detection unit for detecting the coil current; and a current amount detected by the current detection unit is compared with a target value, and when the current amount exceeds a target value, A target value comparing unit that generates a target reaching signal; an off-period measuring unit that generates an off-period elapse signal after a lapse of a certain period from the generation of the target reaching signal; a motor that supplies the coil current in accordance with the target reaching signal An output drive unit that controls the drive transistor to be off, controls the pulse width of the motor drive transistor by controlling the motor drive transistor in accordance with the off-period elapsed signal, and switches a signal corresponding to a level of the coil current. Switching reference comparing means for comparing with a reference value, and generating a switching signal when the current value is lower than the switching reference value. In the period, the motor drive transistors on the power supply side and the ground side are driven on both sides based on the target arrival signal, and the motor drive transistors on the power supply side and the ground side are driven on both sides in response to a switching signal from the switching reference comparing means. A motor drive device characterized in that the drive is switched from one side to one side drive. 3. A motor drive device for supplying a desired coil current to a motor coil by controlling a pulse width of one of a motor drive transistor on a power supply side and a ground side, and for reducing the coil current. In the current off command period, after the start of the off period of the motor drive transistor, the off period of the motor drive transistor is continued until the level of the coil current decreases to a predetermined off target value. A motor drive device characterized by switching from off control to on control. 4. The motor drive device according to claim 1, wherein the off period of the motor drive transistor is constant during the current-off command period, and both sides of the motor drive transistor during the off period. A mix mode in which the drive and the one-side drive are switched and executed, and a level priority mode in which the off period is continued until the level of the coil current decreases to a predetermined off target value, can be set. When set, within a certain off period of the motor drive transistor, the switching control is performed between both-side drive and one-side drive of the motor drive transistor. When the level priority mode is set, both-side drive of the motor drive transistor is performed. And the switching operation between one-side drive and the one-side drive is stopped. A motor driving device, wherein generation of an off-period elapse signal for terminating the off-period of the motor driving transistor is stopped until the reference value is reached.